Gospel = Kingdom

The 'gospel' is the gospel 'of the kingdom'.

We glean the key takeaway truths (about Jesus' death, burial and resurrection being for the forgiveness of the sins of the whole world) from WITHIN a story which in the first instance was more specifically concerned with Israel, and not in a non-kingdom sense either:

Jesus submitted to the Jews who were intent on handing Him over to death at the hands of the Romans in order to avert what they knew would otherwise mean national retribution if they were instead perceived as political revolutionaries.

And even that part of the plot was told by the gospel-writers within an OVER-ARCHING NARRATIVE of what God was doing for Israel:

God was visiting Israel, in the Person of His Son, fulfilling the promise of Abraham, inaugurating the kingdom of God and all that the Kingdom of God entailed as promised in Covenant and Prophecy (forgiveness, healing, restoration, Israel becoming a blessing to all nations, along with judgement, resurrection, the final defeat of evil regimes, and newness in every way).

The 'gospel' was the glad announcement that all of that was now being inaugurated - in Jesus Christ, by His death, burial and resurrection. An announcement to Israel first, and also to all nations.

"God was in Christ, reconciling the world to Himself, not imputing their trespasses to them".

Individual forgiveness, although it's central, was not so much a standalone theme which can be plucked from the gospels and labelled as 'the gospel' while the theme of the 'kingdom' gets dispensed with until later as if the theme of Israel's 'kingdom' is somehow separate from the gospel.

No, what God did in Christ Jesus through His cross and resurrection, was God's way of bringing the 'kingdom' - for Israelis first, and also for all the world.

It's just that there's timing in how some components of the achievement of the cross are to get rolled-out. But even though it's yet to be consummated, it's all already been intrinsically inaugurated, through the cross and resurrection of Jesus.

Kingdom already/kingdom to come.
We are saved - we're going to be saved.
We're raised with Christ - we're going to be raised at His coming.
Evil has been judged - it's going to be finally judged on the last day.

First coming/second coming.

That's the revelation of the New Testament. The 'gospel' - 'of the kingdom'.

It's 'news' and it's 'good'!